The bleaching of photographic silver images using cobalt complexes is generally known in the art. British Pat. No. 777,635, for example, teaches the simultaneous bleaching and fixing of a subtractive color negative using a cobalt aquo-ammine cationic complex and a silver halide solvent as the bleaching and fixing agents. In my U.S. Pat. No. 3,923,511, issued Dec. 2, 1975, I disclose a process for producing a photographic dye image in a monobath. The monobath is comprised of a color-developer solution containing one or more developing agents including at least one color-developing agent and, optionally, a color coupler to which has been added a cobalt(III) complex and a silver halide solvent. Upon processing a photographic element containing a latent image in a silver halide emulsion layer, a silver image is first developed. The silver image is then amplified by an image dye-forming redox amplification reaction in which the cobalt(III) complex oxidizes the color-developing agent using image silver as a catalyst for the reaction. The oxidized color-developing agent then reacts with the color coupler to form a dye image. The silver image is bleached by excess cobalt(III) complex, and the silver halide is fixed by the silver halide solvent so that the photographic element leaving the processing monobath bears a photographic dye image but lacks a corresponding silver image. In specific, preferred embodiments, the monobaths of my above-cited patent application incorporate sequestering agents, such as ethylenediaminetetraacetic acid, capable of complexing with cobalt(II) to form a soluble reaction product. In this way, any risk of spontaneous oxidation of the developing agent by reoxidized cobalt reaction products is avoided.
The formation of photographic dye images through the use of peroxide oxidizing agents is also generally well-known in the art. For example, Matejec, U.S. Pat. No. 3,674,490, issued July 4, 1972, teaches the forming of a photographic silver image which can then be used to catalyze the redox reaction of a peroxide oxidizing agent and a color-developing agent. Useful catalytic materials are not limited to photographic silver images, but include noble metals of Groups Ib and VIII of the Periodic Table generally. Matejec, U.S. Pat. No. 3,776,730, issued Dec. 4, 1973, teaches the use of light-destructible peroxidase and catalase enzymes to catalyze the peroxide redox reaction. British Pat. No. 1,329,444 published Sept. 5, 1973, teaches forming a peroxide redox reaction catalyst by imagewise-exposing a simple or complex salt of a heavy metal of Group VIb, VIIb or VIII of the Periodic Table with a mono- or polybasic carboxylic acid. Weyde et al., U.S. Pat. No. 3,684,511, issued Aug. 15, 1972, teaches imagewise-exposing an iodoform or derivative compound to form a catalyst imagewise.
One of the significant disadvantages encountered in using peroxide redox reactions to generate photographic dye images has centered around the necessity of providing a clean catalyst surface. This is pointed out in Research Disclosure, Volume 116, Item No. 11660, titled "Image Amplification Systems", published December, 1973. A number of materials are disclosed which tend to become adsorbed to the surface of catalytic noble metal nuclei and thereby to interfere with peroxide oxidizing agent redox reactions with color-developing agents. These include adsorbed stabilizers, antifoggants and spectral-sensitizing dyes. Azoles and thiazoles which are free from mercaptan and ionic iodide moieties are taught to be useful without fouling catalytic surfaces. Mercaptotetrazoles, -oxazoles, and -imidazoles are taught to be avoided. Since peroxide-containing amplifier solutions may be poisoned by bromide ions or antifoggants carried over from conventional development solutions, it is taught to limit developing solutions to potassium bromide or antifoggant concentrations no greater than 1 gram per liter.